My center post was constructed from 1" inner diameter
Schedule 40 pvc tubing 52" long that I had from another project.
Allow 12 inch or a bit more if you like to extend below the bottom
of the baseplate. You will need 40" of pvc tube to
extend above the top of the baseplate which also include the 1 inch
that goes through the floor flange. See center post
picture. Also notice that I drilled a hole and placed a bolt through the
floor flange and pvc tubing to help prevent the tubing
from turning.

Place mouse over image for a larger
view. Center
Post.

Preparing the center post for all feed line
and driven element connections. If you are building a 5 band Hex
Beam you will need to drill 10 holes 1" inch apart. I used 1" 8/32
brass screws, nuts and washers for the terminal connections. You
will also need a clothes hanger to fish the screw through the
inside of the pvc tubing, unless you choose another method of
making your feed points. Picture below shows how to use the
clothes hanger to fish the screws inside the tubing.
Once holes are drilled for all the bands you plan to use, e.g. 10, 12, 15 meters band side. Start with the 15 meter band and
work your way out toward the 10 meter band. Then from the other
side start with the 17 meter band and work out toward the 20 meter
band. It will take a little time.
Fishing screws inside pvc tubing.

Drilling out the holes for our 5 band Hex
Beam. Measuring 40" of tubing starting from the baseplate to end of
the tubing. Measure 7" from the base up the tubing will
be for the 10 meter band.
Measure 11" from the base up the tubing will be for the 12 meter
band.
Measure 15" from the base up the tubing will be for the 15 meter
band.
Measure 19" from the base up the tubing will be for the 17 meter
band.
Measure 36 1/2" from the base up the tubing will be for the 20
meter band.
Hopefully the photo below will give you some idea where each band
section is located.
Location of band section

Another view of what your coaxial feed point
terminal connections should look like once you've finish fishing
the screw through Fig1. Fig2 Shows center post with coax connected.
Your main coax feed line is connected at the top of the center
post. Do not wire your center post with solid copper wire like in
fig 1. I was trying something out. This does not work. Swr was very
high when using this arrangement. You will need to cut all coax to
length such as in fig 2. This can take some time to do. Coax used
was RG 213. You can used LMR400 which I started to purchase or any
good coax.

Fig 1
Fig 2
Seal all coax connection to keep water out with either liquid tape
or silicon. I used silicon because I had some around.

Feeding your coax through the baseplate to
the top of the center post, and connecting it to the 20 meter terminal
connections. Use cable tie to fasten coax to center post. You
may also want to create a coaxial balun using about 6 turns of your
coax and 6 inch in diameter. My balun is a part of my feed line one
continues run of cable.